The mismatch sign is thought to reflect microcystic changes,43 and has been found only in lower grade gliomas.41 Although specificity is high, suggesting that the T2-FLAIR mismatch sign is a reliable indicator of IDH-mutant 1p19q intact astrocytomas, the sensitivity is variable and effect on clinical course is uncertain.40,42. The gene discussed is IDH2; the disease is astrocytoma (excluding glioblastoma).